Alarm systems that report the existence of an emergency condition, such as fire, intrusion, holdup, high water, procedure failure, etc., by means of an electrical circuit using wires connected between the protected location and an alarm reporting point, have been in common practice for nearly a century. The vast majority of these have utilized telephone circuits for connection between a protected location and an alarm reporting center. However, there have always been and continue to exist locations, because of their temporary nature, distance from telephone service or remoteness, for which wired alarm protection is not possible or practical.
Alarm systems that signal the existence of an alarm condition without using wire conductors by employing radio transmission are presently well established practice, but, like any VHF or UHF radio system, in order to guarantee a reliable signal, the transmitter antenna signaling the alarm and the receiver antenna intended to receive the alarm should be on as close to an optical line-of-sight path as possible. In practice, this is seldom achievable, so that tall antenna support structures are employed and receiving locations are specially selected for being on high ground or in tall buildings. Add to this the possibility of irregular topography, intervening structures and mandated low transmitter power and the result is, in reality, limited distance between the protected site and the alarm receiving point. In the very instances where a radio alarm system would be best employed, these technical problems have prevented its use.
This invention attacks all of the above shortcomings of existing radio alarm systems and thereby increases the effective range manifold.
It is well known to provide a flare piston or rocket, adapted to propel or project a pyrotechnic device to a high elevation, to aid in marine or air searches and rescues. However, such devices are limited to situations where a rescuer is sufficiently near to be able to observe the signal which is emitted. In addition, the signal which is emitted gives no identification, either of its sender or of the nature of the difficulty encountered.
Prior U.S. Pat. No. 2,519,123 to Dwyer et al describes one such pyrotechnic device equipped with a parachute to reduce the rate of descent of the device and increase the likelihood of its detection.
A Rasmussen at al U.S. Pat. No. 3,432,857 describes a rocket-propelled shell which contains an amount of chaff capable of reflecting a radar beam. When the shell reaches a certain altitude, the chaff is discharged to form a radar beam-reflecting cloud capable of detection. The patent discusses a problem with conventional radio transmitters adapted to transmit a homing signal, namely, the need for at least two receiving stations in range of the transmitter capable of fixing on the location of the transmitter. As with a pyrotechnic device, the signal given provides no identification either with regard to the identity of the sender or the nature of the difficulty encountered.
A Zworykin et al U.S. Pat. No. 3,038,154 describes a missile which contains, among other components, a radio transmitter adapted to transmit a radio signal to a ground receiver. The missile is provided with a parachute to slow its descent. The apparatus of the Zworykin et al patent is especially adapted for meteorological observations by exploring charged areas in the atmosphere in or near clouds and moving air masses. The apparatus is not concerned with, nor suitable for, detecting and signaling the existance of an alarm condition at a remote site.